1. Field of the Invention
The present application relates to a device for implanting objects and, more particularly, to a device for implanting objects into animal tissue.
2. Description of the Related Art
There is growing interest in biomedical research for applications of sustained-release pellets, which are implanted sub-dermally as an alternative method of daily or multi-weekly drug injection/administration. Daily injections ensure daily stress and pain for the research subject while increasing the workload for the researcher. Current methods of liquid substance (drug) delivery by injections fail to hold the research subject at a constant therapeutic dose due to peaks and troughs associated with injections. Fortunately, sustained-release pellets are presently used in research animals, household pets, and food-producing farm animals.
A few classifications of drugs that are currently manufactured for use in sustained-release pellet form include antibiotics, steroidal and non-steroidal anti-inflammatories, other analgesics, hormones, and antioxidants. Companies, such as Innovative Research of America, customize pellets for research use based on shape, size, dosing, release rates, and length of study, thus benefiting the researcher and research subject by replacing multiple injections with less frequent subdermal pellet implants.
A trocar (http://www.innovrsrch.com/trochar.asp) is the device currently used for pellet implantation in rodents. However, the trocar can be difficult to use (often requiring two people for successful execution into a research animal), inaccurate, and non-sterile. The major difficulty with the trocar is that it lacks a mechanism to hold the pellet in a secure and sterile manner during pellet implantation. Pellet implantation using the trocar often requires multiple attempts due to dulling of the device with repeated use, which can result in failure to break the skin, poor pellet placement, and the pellet falling out of the device and into the bacteria-covered coat hair of the animal. Due to the complications of this procedure, one must restrain the animal repeatedly, sometimes leading to multiple incisions due to inaccuracy of pellet implantation and lack of device control, which can contribute to an increase in subcutaneous nonspecific inflammation for the research subject and holds potential to falsify the true outcome of the research study.
Kersco's U.S. Pat. No. 4,105,030 describes an intricate delivery device for implanting multiple pellets. Though multiple pellets can be loaded into the gun-like device and held in the device with a valve until delivery, multiple pellets cannot be implanted at one time as individual pellets must be forced through a slit in the valve. Kersco's slit design also subjects the pellets to compression stress thereby compromising the integrity of the pellet(s). Additionally, the bulk and proportion of the device, with respect to a small animal research subject, may be difficult to maneuver and operate resulting in an exertion of unnecessary force on the subject thereby leading to poor pellet placement or injury to the animal.
U.S. Pat. No. 5,810,769 to Schlegel (1998) and U.S. Pat. No. 5,281,197 to Arias (1994) aimed to correct problems arising from a device whose pellet(s) cannot be restrained before the desired time of implantation. These patents suggested decreasing the diameter of the cannula and increasing the diameter of the pellet so that the pellet is held in the device until it is forced through the cannula. Unfortunately, solving one problem has created another in that the integrity of the pellet(s) is now subject to degradation. A pellet with a diameter larger than the cannula is mechanically forced through the cannula, and therefore, a portion of the substance to be delivered into the subject, is lost to compression strain. Schlegel notes that this type of pellet restraining mechanism requires pellets with elastic properties as not to compromise the contents of the pellet. If the pellets are not of an exact size, with a diameter barely larger than the narrowed cannula, there is a risk for device failure, specifically if the pellets are too small in diameter and they cannot be contained within the narrowed portion of the cannula, or, conversely, if the pellet diameter is so large that the pellets cannot be mechanically forced through the narrowed cannula without excessive damage to the integrity of a pellet with, and especially, without, elastic properties. Essentially, Schlegel's device is limiting in application and use of as the device requires inserted objects to contain elastic properties or be uncompromised by compression strain.
Another patent of similar interest is U.S. Pat. No. 7,104,945 to Miller (2006). Miller's device is intended to improve upon previous strategies to retain an object in the delivery device prior to implanting the pellet into tissue without the use of bone wax. Specifically, the pellet and spacers (brachytherapy procedure) are held by flexible tabs and are forced passed the tabs to allow the pellet to pass into the tissue. This device can hold multiple objects, however each implantation yields a decrease in mechanical function as tabs are flexed multiple times leading to an increasing margin of error and a decrease in function and accuracy (and timing) of delivery. In Miller's device, the spacers appear to be significantly larger in diameter than the seeds, which raises the concern of the spacers compromising the integrity of the flexible tab to the extent that the comparatively smaller pellet can no longer be contained using the tab, resulting in failure of the retaining mechanism and inaccurate delivery of the pellet. Conversely, if the retaining tab is too stringent, the tab, itself, could compromise the contents of the pellet, especially if the pellet does not posses elastic properties to avoid damage incurred from the compression strain of forcing the pellet passed the tab.
Prior devices capable of retaining an object in a device to maintain control of the object prior to reaching the desired site of implantation have overcomplicated the function of the device and/or included a counterproductive mechanism which can alter the integrity of the object's contents upon implantation. Consequently, there exists a need for a device that can efficiently and effectively deliver objects into subjects without damaging the objects or decreasing effectiveness when delivering more than one object per procedure.